The prior art teaches electrical load control systems in which the actual rate of power delivered to a plurality of loads is continuously measured and compared with a predetermined rate of power consumption, sometimes referred to as a set point. If the actual rate exceeds the set point, then one or more of the loads are disconnected (shed) to decrease the actual rate of power consumption. If the converse exists, then one or more of the loads are connected (added) to increase the actual rate of power consumption.
The preferred application for such electrical load control systems lies in the regulation of power consumption by electrical utility customers. As is well known, the charge made to each utility customer by the utility is dependent not only on the total energy consumption over a substantial period of time, such as a month, but also on whether or not the total energy consumption over any one of a succession of shorter time periods, referred to as demand intervals, has exceeded a maximum energy demand established by the utility.
When used in such applications, the electrical load control systems may include a power monitoring and regulating circuit which produces an analog signal representing the actual rate of power being consumed by a plurality of loads at the customer's facility. The analog signal is compared within the power monitoring and regulating circuit with a reference signal representing a predetermined rate of power consumption, or set point. When the analog signal exceeds or is less than the reference signal, the power monitoring and regulating circuit functions to produce output signals for effecting load control. These output signals are supplied to a load control circuit that is adapted to control the on/off states of the plurality of loads at the facility. As an example, the output signals may be in the form of one or more shed pulses that direct the load control circuit to shed a load for each shed pulse, with the number of shed pulses being related to the amount by which the actual rate of power consumption exceeds the predetermined rate. Similarly, when the actual rate of power consumption is less than the predetermined rate, one or more add pulses are produced, each such add pulse directing the load control circuit to add one load. The load control circuit may include provisions for determining the sequence in which the plurality of loads at the facility are to be added or shed in accordance with the add and shed pulses from the power monitoring and regulating circuit. For example, a priority sequence may be established in which certain essential loads, such as air conditioning equipment or the like, are shed only after other loads, such as lighting, have been shed, and in which such essential loads are added before such other loads are added. Provision may also be made for adding and shedding certain other loads in a variable, rotating order in response to the add and shed pulses.
The set point, or predetermined rate of power consumption, typically is manually adjusted to represent a maximum, average rate of power consumption that will not permit the total energy consumption over the demand interval to exceed the maximum energy demand established by the utility. As a result, the electrical load control system functions to maintain total energy consumption over each demand interval below the maximum energy demand, and also functions to optimize energy usage at the facility by acting to shed nonessential loads.
However, when the actual rate of power consumption drops substantially below the set point over a relatively long period of time, it will be seen that the electrical load control systems of the prior art do not function to optimize energy usage at the facility, inasmuch as many nonessential loads will be maintained in an on status. This situation typically occurs due to seasonal variations in total energy consumption most often occasioned by a reduction in the amount of power consumed by air conditioning equipment and a reduction in the number of lighting loads.
In such a situation, energy usage can be optimized by lowering the set point to represent an average rate of power consumption consistent with the actual rate of power consumption. However, with the electrical load control systems of the prior art, the customer must physically go to the unit embodying the power monitoring and regulating circuit to lower the set point. Since the decrease in the rate of power consumption occurs over a relatively long period of time, the customer may not realize, for a substantial period of time, that the set point needs readjusting, and even then may not act to readjust the set point. Further, if the set point is lowered, it will be appreciated that a relatively rapid increase in the actual rate of power consumption at the facility will cause the electrical load control system to unnecessarily shed loads, including essential loads, even though the maximum, average rate of power consumption permitted in the demand interval has not been exceeded. As a result, it has been found that the customer usually will not attempt to readjust the set point in periods of lowered energy consumption, thereby resulting in the electrical load control system providing little or no control of the plurality of loads during that time.
It is therefore an object of this invention to provide a floating set point control circuit and method which allow a set point of an electrical load control system to vary from a previously established set point value in a predetermined manner designed to optimize energy usage of the plurality of loads at a facility.
It is another object of this invention to provide such a control circuit and method which allow the set point to decrease at a gradual rate from a previously established set point value during times of relatively low power consumption.
It is yet another object of this invention to provide such a control circuit and method which permit the set point to rapidly increase toward the previously established set point value under certain conditions representing a rapid increase in power consumption.
It is a further object of this invention to provide such a control circuit and method which allows the set point to decrease from a previously established set point value as long as a control load, typically an essential load at the facility, is in an on state, and which permits the set point to rapidly rise toward the previously established set point value when the control load is in an off state.
It is still a further object of this invention to provide such a control circuit and method in which the set point incrementally decreases from and incrementally increases to a previously established value in a predetermined range.
It is yet a further object of this invention to provide such a control circuit in which the rate of set point decreases, the rate of set point increase, the range of set point reduction, and the identity of the control load, are all individually selectable.